1. Field of the Invention
This invention relates to a stepping motor to be used in various apparatus such as floppy disc driving devices, printers and automatic devices.
2. Description of Prior Art
FIG. 1 is a perspective view of a stator of a conventional stepping motor, and FIG. 2 is a sectional view of the stepping motor. As shown in the drawing, the stepping motor has a rotor 2 fixed to a rotor shaft 1 which is rotatably supported by a bearing 3 in co-operation with an E washer 4 and a wave washer 5. Stator plates 8, 9, 10 and 11 are arranged in an equally spaced apart relation along a cylindrical surface formed around the rotor shaft 1, in a manner such that the stator plates 8 and 9 as well as 10 and 11 are displaced from each other by an electric angle of 90.degree., while the stator plates 9 and 10 are displaced from each other by an electric angle of 45.degree.. The stator plates thus arranged are secured to a housing 6 of the stepping motor.
The stepping motor further comprises coil windings 14 and 15 wound around bobbins 12 and 13 are placed between the stator plates 8 and 9, and 10 and 11, respectively. By energizing the coil windings 14 and 15 in an appropriate sequence and direction, the stator plates produce a magnetic field which rotates the rotor 2 of the stepping motor in a clockwise or a counterclockwise direction.
In the above described construction of the conventional stepping motor, since the rotor shaft 1 is rotatably supported by the single bearing 3, a slight gap or play existing in a direction perpendicular to the shaft 1 tends to rotate the rotor 2 in a swinging manner, thus making it difficult to maintain a constant gap between the rotor 2 and the stator plates 8 through 11. That is, when a force is applied perpendicularly to the rotor shaft 1, the force tends to tilt the rotor shaft 1 relative to the axis of the stepping motor, thus rendering the gap between the rotor 2 and the stator plates 8 through 11 to be uneven. The tilting of the rotor shaft 1 adversely affects the torque and the precision in operation of the stepping motor, and makes it difficult to assure satisfactory operation of the stepping motor.